Recently, portable electronic devices such as smart phones, tablets, and mobile PCs have been widely used. Meanwhile, the electronic devices have a tendency that the heating value generated in electronic circuits mounted inside the electronic devices increases with the implementation of the high-speed processing capability and the diversification of the processing. Since an electronic circuit, especially, an integrated circuit is a heating element that generates a large heating value, a case temperature near the heating element inside an electronic device may locally increase. Thus, there is a demand for dissipating or distributing the heat generated from the heating element to suppress the local increase of the case temperature of the electronic device.
As a method of suppressing the local increase of the case temperature, there is a method of providing a heat pipe inside the case of the electronic device to transport the heat generated in the electronic circuit to a heat sink. Here, descriptions will be made on the installation of a heat pipe 1 when the electronic device is a smart phone 10, using FIGS. 1A to 2B.
FIG. 1A is an exploded perspective view illustrating a mounting position of a heat pipe 1 in the smart phone 10 of a comparative technology. The smart phone 10 includes a heat sink plate 4, a board 5, and a battery 6 inside a case 3 provided with a touch panel 2, and a rear cover 7 for sealing the rear side of the case 3. FIG. 1A illustrates a state where a component 8A is mounted on the surface of the rear cover 7 side of the board 5, and a heating element 8 is mounted on the surface of the heat sink plate 4 side of the board 5. The component 8A is a common integrated circuit (IC) and may or may not generate heat. Descriptions of the component 8A are omitted herein.
One end of the heat pipe 1 is superimposed on the heating element present on the heat sink plate 4 side of the board 5, and the other end thereof is curved and disposed along the lateral surface of the battery 6 in order to circumvent the mounted component. FIG. 1B is a perspective view illustrating a state where the heat pipe 1, the board 5, and the battery 6 illustrated in FIG. 1A are attached to the case 3 of the smart phone 10, and represents the position of the heat pipe 1 by a dashed line.
FIG. 2A is a sectional view illustrating an installation position of the heat pipe 1 for dissipating the heat of the heating element 8 mounted on the board 5 in the comparative technology, and illustrates a partial sectional view of the smart phone 10 of FIG. 1B taken along the line X-X in FIG. 1B. However, FIG. 2A illustrates only the heating element 8 mounted on the heat sink plate 4 side of the board 5 and omits illustration of the component 8A on the rear cover 7 side of the board 5.
The heating element 8 mounted on the board 5 is generally a central processing unit (CPU). A shield frame 11 is provided around the heating element 8 in order to avoid the influence of electromagnetic waves, and the opening side of the shield frame 11 is sealed by a shield cap 12. When the heat generated from the heating element 8 is dissipated by the heat pipe 1, the heat pipe 1 is installed between the shield cap 12 and the heat sink plate 4. In this case, heat conducting sheets 13 are provided between the heating element 8 and the shield cap 12 and between the shield cap 12 and the heat pipe 1 so that the heat conduction from the heating element 8 to the heat pipe 1 is improved.
Meanwhile, since electronic devices are becoming smaller and thinner, there is a demand for reducing a distance D between the external side of the board 5 and the external side of the heat sink plate 4 when the electronic devices use the heat pipe. Accordingly, in order to reduce the space for mounting the heat pipe, a thin heat pipe 1A of which the thickness is thinned by increasing the flatness of the heat pipe 1 is used as illustrated in FIG. 2B. By using the thin heat pipe 1A, the distance (d) between the external side of the board 5 and the external side of the heat sink plate 4 may be made shorter than the distance D when the ordinary heat pipe 1 is used.
However, since the thin heat pipe 1A is formed by crushing the heat pipe 1, the heat is hardly transferred when the heat pipe 1 is excessively crushed, and thus the heat conducting effect of the heat pipe 1A is reduced. Further, since the heat pipe 1A is curved to guide the heat of the heating element to the heat sink, the length of the heat pipe from the heating element to the heat sink is long. Accordingly, heat is hardly transferred in the thin heat pipe, and thus the heat conducting effect of the heat pipe is reduced.
The following is a reference document.    [Document 1] Japanese Laid-Open Patent Publication No. 2015-95629.